Method of offset explosive stimulation

ABSTRACT

A production borehole is drilled to total depth into and through a producing formation and casing is set to an intermediate depth. A bridge plug is set below the casing shoe into the open hole section above the producing formation and one or more offset wells are drilled into the producing formation beginning at the open hole section of the production borehole between the casing shoe and the bridge plug. The offset holes are loaded with explosive, plugged off, gravel packed and detonated in order to stimulate the well bore and surrounding formation.

lee/ 3080 05-01-73 X'R 397309274 United States Patent 11 1 1111 3,730,274 Brown 5] May 1, 1973 [54] METHOD OF OFFSET EXPLOSIVE 3,587,743 6/1971 Howard ..166/299 STIMULATION 3,616,855 11/1971 Colgate ..l66/299 X [75] Inventor: Larry P. Brown, Tulsa, Okla. Primary El'mminer David H Brown [73] Assignee: Cities Service Oil Company, Tulsa, Richard Geamfln Okla.

[57] ABSTRACT [22] Filed: Dec. 30, 1971 I A produc t1on borehole 1s drilled to total depth into 1 1 PP 214,053 and through a producing formation and casing is set to w an intermediate depth. A bridge plug is set below the 52 us. c1 ..l66/299 166/308 Casing ShOe mm the Swim the [51] Int Cl Ezlb 43/26- producing formation and one or more offset wells are [58] Field 299 305 drilled into the producing formation beginning at the open hole section of the production borehole between the casing shoe and the bridge plug. The offset holes are loaded with explosive, plugged off, gravel packed [56] References cued and detonated in order to stimulate the well bore and UNITED STATES PATENTS Surrounding f 1,422,204 7 1922 Hoover ct a1. 166/299 x 3 Claims, 2 Drawing Figures 3,002,454 /1961 Chesnut "166/299,

\ggs l Patented May 1, 1973 3,730,274

2 Sheets-Sheet 1 l NVEN TOR.

L RR) P. BROWN BY Mn Patented May 1, 1973 2 Sheets-Sheet 2 //////A/ /M////// ////////m E E FIG. 2

INVENTOR. LA RY ROW/V A 7'TORNEY 1 METHOD OF OFFSET EXPLOSIVE STIMULATION BACKGROUND OF THE INVENTION The present invention relates to a method of offset explosive stimulation for wellbores. More particularly, the method of the present invention provides an explosive stimulation technique wherein multiple wellbore connections are utilized in order to further extend stimulation within a formation. 7

The stimulation of oil and gas wells by explosives has long been practiced in the petroleum industry. .Two methods have been basically utilized for the stimulation technique. A first method, being an old method, is a borehole stimulation technique requiring drilling and completion of a well followed by loading of the borehole with an explosive charge and detonating the charge, thereby stimulating the fonnation adjacent to the wellbore. A newer and second method is the fracture extension concept which calls for drilling, completing and fracturing a wellbore. A slurry type explosive is pumped into the fractures and detonated, thus augmenting the previous fracture treatment. Both methods have the same serious economic drawback in that the cost of well cleanout prior to putting the well into production after stimulation is high. No method has been found economically satisfactory for explosive stimulation of relatively shallow and inexpensive wellbores. However, many deep producing formations are amenable to explosive stimulation, but the cost of completed through the remainder of the wellbore such that the well may be placed on production into the fractured and stimulated area thereabout. I

BRIEF DESCRIPTION OF THE DRAWINGS cased and completed subsequent to the explosive stimulation technique depicting a fractured zone about the wellbore formed through the stimulation program.

drilling explosive boreholes from the surface makes offset explosive stimulation economically unattractive.

What is required is an economic and feasible method for offset explosive stimulation of wells, particularly those wells drilled within shallow formations.

It is an object of the present invention to provide a method for the offset explosive stimulation of wells.

It is a further object of the present invention to provide an offset explosive stimulation technique wherein multiple boreholes are connected therein a production borehole in order to provide a network for loading explosive charges and stimulating the formation about a wellbore.

With these and other objects in mind, the present invention may be more readily understood through referral to the following drawing and accompanying discus- SUMMARY OF THE INVENTION The objects of the present invention are accomplished through utilization of a method for offset explosive stimulation of a wellbore and surrounding formation. The method comprises drilling a main well to total depth through the formation to be stimulated. The well is cased and completed to a depth above the formation to be stimulated and a bridge plug is placed in the main drilled wellbore above the formation to be stimulated, but below the cased and completed portion of the wellbore. One or more offset wells are drilled through the uncased portion of the main wellbore below the casing string, but above the bridge plug and into the formation to be stimulated. The offset wells are charged with explosives through a portion of the offset well exposed to the formation for stimulation and packed above the explosive charge up to the entrance of the offset well into the main wellbore. The explosive charge is detonated and the bridge plug removed with casing being DETAILED DESCRIPTION OF THE INVENTION The present invention may be more readily understood by referral to the accompanying Figures in which FIG. 1 depicts wellbore 22 drilled from the earths surface 12 through overburden 14 into formation 16 of interest which is to be stimulated through the process of the present invention. The main wellbore 22 is cased and completed by casings string 18 and cement sheath 20 from the earths surface to a point above the formation to be stimulated. A bridge plug 24 is positioned therein the wellbore above the formation to be stimulated, but below the cased and completed portion of the main wellbore 22 so as to leave a section of uncompleted wellbore 26 open between the bridge plug 24 and the cased and completed wellbore 22 through which at least one or more offset wells 28 may be drilled. For the offset well, stimulation process of the presentinvention, explosive charge 34 is loaded into each of the offset wells 28 and a packer 30 is placed thereupon the upper portion of the explosive charge in order to isolate the formation to be stimulated 16. A gravel or sand pack is 32 positioned within offset well 28 upon the packer 30 in order to tamp the charge 34 and allow for the confinement of the explosive as it is detonated.

Now referring to FIG. 2, the stimulated formation and wellbore are depicted wherein the explosive charge has been detonated in order to form a rubblized offset well 28 and a fracture zone 36 within the stimulated formation 16,. The main wellbore .22 is completely cased and completed through casing string 18 and cement sheath 20 through the formation stimulated l6 and having perforations 44 therein in order to provide for productive flow of fluids from the stimulated formation 16, particularly from the fractured zone 36 into the wellbore -22. The wellbore 22 is isolated by a production packer 38 having a tubing string 40 contained therein .with a wellhead production string 42 for removal of the producing fluids from the stimulated formation 16 through wellbore 22 passing through overburden 14 to the earths surface 12. It is noted that the offset wells 28 are completely isolated from the wellbore 22 by the casing string 18 and cement sheath 20 such that the wells are expendable and utilized only after the explosive charge is loaded in the offset wells.

material required. It is also preferred in the utilization of the process of the present invention, that non-autodetonating explosives be utilized so that a safe material may be placed within the offset wells 28 in order to provide a safe mechanism for the explosive stimulation of the main wellbore. The conventional completion and perforation technique may be utilized in order to complete the wellbore after the offset wells have been detonated. With the shock propagation of the compressive waves from the offset wells to the main well providing for the major fracturing of the formation and the tensive waves reflected by the main wellbore providing a further fracture network to be formed within the formation for adequate stimulation thereof.

Therefore, through utilization of the process of the present invention, one is provided with means for stimulating a wellbore through offset wells particularly in shallow formations in order to provide a stimulated formation wellbore for economic and continued production from the formation.

While the invention has been described above with respect to certain embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth herein.

Therefore, I claim:

1. A method for offset explosive stimulation of a 5 wellbore and surrounding formation, which comprises:

a. drilling a main well to total depth through the formation to be stimulated;

b. casing and completing the drilled wellbore to a depth above the formation to be stimulated;

c. placing a bridge plug in the main drilled wellbore above the formation to be stimulated, but below the completed portion of the wellbore;

d. drilling one or more offset wells through the cased main wellbore and portion of the uncompleted wellbore above the bridge plug and to total depth through the formation to be stimulated;

e. charging the offset wells with explosive through a portion of the offset well exposed to the formation to be stimulated; I

f. packing the offset wells above the explosive charge up to the entrance into main wellbore;

g. detonating the explosive charge; and

h. removing the bridge plug and casing and completing the remainder of the main well.

2. The method of claim 1 wherein the offset wells are packed with sand and gravel.

3. The method of claim 2 wherein the explosive charge is non-autodetonating. 

1. A method for offset explosive stimulation of a wellbore and surrounding formation, which comprises: a. drilling a main well to total depth through the formation to be stimulated; b. casing and completing the drilled wellbore to a depth above the formation to be stimulated; c. placing a bridge plug in the main drilled wellbore above the formation to be stimulated, but below the completed portion of the wellbore; d. drilling one or more offset wells through the cased main wellbore and portion of the uncompleted wellbore above the bridge plug and to total depth through the formation to be stimulated; e. charging the offset wells with explosive through a portion of the offset well exposed to the formation to be stimulated; f. packing the offset wells above the explosive charge up to the entrance into main wellbore; g. detonating the explosive charge; and h. removing the bridge plug and casing and completing the remainder of the main well.
 2. The method of claim 1 wherein the offset wells are packed with sand and gravel.
 3. The method of claim 2 wherein the explosive charge is non-autodetonating. 